(1) Field of the Invention
The present invention relates to an adhesive composition and more particularly, the one which can effectively adhere a vulcanized rubber to another vulcanized rubber or to another material.
(2) Description of the Prior Art
It is generally difficult to adhere a vulcanized rubber to another vulcanized rubber or to another materials.
As a method for adhering a vulcanized rubber, it has been proposed that a surface have applied a solution of an unvulcanized rubber in an organic solvent, such as toluene, that is a rubber cement and dried, and then the thus treated vulcanized rubber and an unvulcanized rubber are superimposed, pressed and vulcanized to adhere the unvulcanized rubber, but there is a disadvantage that a mold must be provided for each molding and, further, a complicated mechanical apparatus is necessary for pressing and heating. Furthermore, the unvulcanized rubber to be used is limited to the same kind as the vulcanized rubber.
As another method, it has been proposed that a rubber cement obtained by dissolving unvulcanized polychloroprene (CR), acrylonitrile-butadiene copolymer rubber (NBR), generally referred to as "nitrile rubber", a graft copolymer rubber obtained by grafting a vinyl compound, such as methyl methacrylate, to the above described rubbers or blends of these rubbers with phenolic resins, in an organic solvent, is used for adhering the mutual vulcanized rubbers or a vulcanized rubber to the other material, but this method cannot provide a satisfactory adhesion.
The inventors have already found and proposed the novel method for adhering the mutual vulcanized rubbers or a vulcanized rubber to another material in which the surface of the vulcanized rubber is previously treated with various compounds, such as, iodine isocyanate, active halomethyl ether, sulfur halide, sulfenyl halide, N,N-dihaloalkyl urethane or N,N-dihaloaryl sulfonamide and the thus treated vulcanized rubber is adhered by means of an ordinarily used adhesive. However, this method has the following disadvantage. That is,
(a) the specimens to be bonded together are apt to shift before the adhesive is completely hardened or are apt to warp after the adhesion is completed, because of low stickiness or large fluidity of the adhesive to be used in this method, such as a polyurethane elastomer or epoxy resin, and
(b) for example, in a polyurethane adhesive, it is necessary to permit it to stand more than one day at room temperature (22.degree. C.) until the highest adhesion is obtained.